In a manufacturing process of semiconductor devices or liquid crystal boards, a chemical agent such as a photoresist liquid is used. For example, to apply the photoresist liquid on a surface of a semiconductor wafer in the manufacturing process of semiconductor devices, the photoresist liquid is dropped on the surface of the semiconductor wafer in a state of rotating the semiconductor wafer in a horizontal plane. As a chemical liquid supply apparatus used for application of the photoresist liquid, there is developed a pump of such a type that a flexible tube is incorporated in an apparatus body and an expansion/shrinkage chamber is formed inside the flexible tube and a pressurizing chamber is formed outside the flexible tube, as conventionally disclosed in Patent Document 1. The pump of this type is also called a tube pump.
In such a chemical liquid supply apparatus, as disclosed in Japanese Patent Laid-Open Publication No. 11-230048 (Patent Document 1), there are a type in which an apparatus body is formed by a pipe or tube member and a pressurizing medium is supplied from an outside pump to a pressurizing chamber formed between the apparatus body and a flexible tube to vary a volume of the pressurizing chamber, and a type in which the apparatus body containing the flexible tube is provided with a small bellows and a large bellows mutually different in diameter and those bellows are deformed axially to vary the volume of the pressurizing chamber.
Also in either type, by expanding and shrinking the flexible tube to make the flexible tube operate like a pump, a liquid flowing into the tube from an inlet side can be discharged to the outside from an outlet side. The flexible tube includes a flat type, as described in Patent Document 1, in which a flat portion having an oval section formed in an elastic deformation portion of the flexible tube is expanded and shrunk, and a cylindrical type, as described in Japanese Patent Laid-Open Publication No. 2000-234589, in which a plurality of grooves extending axially are formed in a cylindrical elastic deformation portion.
To discharge the liquid from the tube outlet side to the outside, the volume of the pressurizing chamber is increased and the flexible tube is shrunk. Therefore, to keep a discharge rate constant, it is important that the flexible tube should be shrunk at a specific rate depending on an increase in the volume of the pressurizing chamber. Concurrently, to increase the volume of liquid capable of being discharged by one pump operation, it is important to increase a variation in the volume when being shrunk.
Incidentally, as described above, in the flat flexible tube whose elastic deformation portion has an approximately oval section, since the elastic deformation portion is formed by two semicircular portions and two straight portions for linking the semicircular portions, the two straight portions are elastically deformed so as to mainly approach to each other at a time of discharging the liquid, thereby making it possible to change the deformation amount of the flat portion at a specific rate depending on the increase in the volume of the pressurizing chamber. However, as the flat flexible tube is pressurized and shrunk, the straight portions come to contact with each other and even if being further shrunk, the pressurizing amount and the discharge amount cannot maintain a proportional relation therebetween, whereby the discharge amount becomes inaccurate. In addition, since having the long straight portions, the two semicircular portions are deformed on an outer-radial side when pressure is applied from the outside. At this time, a flat portion is deformed and shrunk so that its longitudinal-directional dimension becomes long. Therefore, the diameter of the apparatus body is required to be set large so that the flat portion may not contact with the apparatus body, that is, a housing for accommodating the flexible tube.
Meanwhile, as described above, in a flat tube in which the elastic deformation portion is formed into a cylindrical shape as a whole and a plurality of grooves extending axially are formed on an outer circumference surface thereof, to shrink the elastic deformation portion, each groove is deformed in an inner-radial direction, so that each circumferential width of four arc-shaped portions may be short. Therefore, the tube cannot be shrunk and deformed unless high pressure is applied to the pressurizing chamber. However, if the high pressure is applied for shrinkage and deformation, a pressure change rate of the pressurizing chamber and an elastic deformation rate of the elastic deformation portion may not be made constant depending on the deformation amount of the elastic deformation portion. Besides, discharge precision is influenced by pressure deformation of the housing or another element member between the housing and the pump. Therefore, to decrease the influence from those and enhance the discharge precision, it is preferred to apply smaller pressure to the pressurizing chamber.
To deform the flexible tube so that the discharge rate is constant throughout a discharge process from start to end of discharge, it is preferred to shrink the flexible tube by small pressure. However, since both ends of the flexible tube are fixed to a joint portion of the apparatus body and further the flexible tube is formed by a material such as a fluoro resin, i.e., a material having a smaller rate of elongation than that of silicone rubber or the like, it is necessary to apply larger pressure to the pressurizing chamber in order to deform the flexible tube by reducing the width of the arc-shaped portion. This pressure is not only changed depending on a deformation amount of the flexible tube but also transmitted to the apparatus body located on an outer side of the flexible tube, that is, the housing, which results in loss of the pressure. Therefore, a pressure change rate of the pressurizing chamber and an elastic deformation rate of the elastic deformation portion do not become constant, and these change rates vary depending on the deformation amount of the flexible tube. If there is a difference in the pressure change rates necessary for deforming the flexible tube between the start and end of discharge in the discharge process of the pump, the discharge rate is not made constant in all processes of liquid discharge and the discharge precision deteriorates.
An object of the present invention is to provide a flexible tube capable of discharging the liquid at the specific discharge amount and with high precision from start to end of discharge.